1. Field of the Invention
This invention relates to an electrolytic cell for producing periodates used as oxidizing agents for organic synthesis.
2. Prior Art
Periodates are usually produced by an electrochemical process, not by a chemical process. The electrolytic cell comprises lead dioxide anodes and mild steel cathodes. In practising this method, an acidic iodate solution is circulated in the anodic compartments and sodium hydroxide (or sulfuric acid) solution is added into the cathodic compartments, and thus iodates are electrolytically oxidized to periodates by using the electrolytic cell provided with diaphragms.
In general, porous porcelain and/or ceramic diaphragms are used for electrolysis but these diaphragms are consumed extensively by the strong oxidizing and alkaline solution. High consumption of diaphragms leads to generation of residues, contamination of both electrolytes, and clogging of the electrolyte flow, and hence anode consumption creates such problems as degradation of the anodes and reduction in current efficiency. For that reason, replacement of anodes and diaphragms and cleaning of the electrolytic cell has to be done every 2 to 4 months. Even if expensive diaphragms are used they will be consumed completely within about six months and will need to be replaced with new ones. In addition, as the diaphragms are fragile and possess insufficient resistance to tightening pressure, they need to be reassembled carefully. Also, in the case of applying cation exchange membranes (Japanese Public Disclosure No. 23286/81), the hydrocarbon membrane has insufficient durability, while on the other hand the fluorocarbon membrane is very expensive. Moreover, maintenance of the membrane is troublesome because of the need to perform conditioning and maintain the wettability of the membrane so as to avoid its shrinkage. The cell cover is provided with the air intake holes and cell gas exhaust pipes. The gas generated by electrolysis consists of hydrogen and a small amount of oxygen, and it is discharged to the outside of the cell through exhaust pipes with a large amount of air for safety reasons. In this process, alkali carbonate crystals accompanied by alkali mist clog the exhaust pipes, thus obstructing the outward flow of gas, causing air pollution in the room in which the cell is located, and also increasing the possibility of hydrogen gas exploding in the cell. When the gap between the level of the solution and the cell cover is kept below 100 millimeters, a large amount of mist accompanies the cell gas as it flows into the exhaust pipes and hence the exhaust pipes require cleaning every 2 or 3 days.